Safety and Efficacy Evaluation of Recombinant Marek’s Disease Virus with REV-LTR

Abstract

Recently, chickens vaccinated with the CVI988/Rispens vaccine showed increased tumor incidence. Moreover, many strains of Marek’s disease virus (MDV) that were naturally integrated with the long terminal repeat (LTR) of the avian reticuloendotheliosis virus (REV) have been isolated, which means it is necessary to develop a new vaccine. In this study, two LTR sequences were inserted into Rispens to construct a recombinant MDV (rMDV). Then, the safety and efficacy of rMDV were evaluated separately in chickens. The growth rate curves showed that the insertion of REV-LTR into MDV enabled a faster replication in vitro than Rispens. Chickens immunized with high or repeated dose rMDV had no MD clinical signs. Further, no tumor, tissue lesions, or evident pathological changes were observed in the chicken organs. Polymerase chain reaction (PCR) and virus isolation revealed that rMDV had the ability to spread horizontally to non-immunized chickens and had no impact on the environment. After five passages in chickens, there were no obvious lesions, and the LTR insertion was stable. There were also no deletions or mutations, which indicates that rMDV is safe in chickens. In addition, rMDV has an advantage over Rispens against vvMDV Md5 at low doses. All results demonstrate that the transgenic strain of rMDV with REV-LTR can be used as a live attenuated vaccine candidate.

Occurrence of Marek's disease in vaccinated Algerian broiler breeder flocks: A histopathological survey

“…The field farms included in the present study included vaccination with the bivalent vaccine comprising HVT and Rispens, which offer greater protection compared to HVT alone. Several researchers [ 18 - 20 ] have reported the effectiveness of the Rispens vaccine in protecting against tumors. However, in the present study, severe tumors were observed in the flocks vaccinated with the Rispens valence.…”

Genomic Medicine and Advances in Vaccine Technology and Development in the Developing and Developed World

“…Infections in stock and cattle increase the risk of starvation; thus, vaccination programs in animals have been encouraged. For such purpose, Song et al [ 11 ] demonstrated that recombinant Marek’s disease virus (rMDV) with reticuloendotheliosis virus (REV)-LTR (long terminal repeat) shows a good safety profile in target chickens and environment and can be used in the development of a vaccine against MDV. An interesting program, as discussed by Antenucci et al, used outer membrane vesicles to immunize chickens against Gallibacterium anatis , which was proven both effective and economically advantageous [ 12 ].…”